This invention relates to the winding of web rolls, and particularly to a method and apparatus for controlling the density or hardness of the rolls during the winding operation.
Typically, a surface type winder employs a rider roll or pressure roll to control the density or hardness of the winding roll of web material. The rider roll is either loaded or its weight relieved, usually by hydraulic or pneumatic cylinders, as the winding roll builds. The operator controls the winding roll's hardness by adjusting the pressure the rider roll exerts during winding by controlling these hydraulic or pneumatic cylinders. This can be a fixed contact pressure throughout the roll's build-up or the contact pressure can be varied on a straight line basis or by means of a curved cam to vary, usually to reduce, the hardness or density according to a predetermined formula or pattern as the roll builds and increases in diameter.
One problem associated with prior art rider roll control systems is their inability to control accurately and continuously the rider roll pressure throughout the winding process, from the very beginning to the end. Those prior art systems that employ a cam to control the rider roll pressure as a function of roll diameter, for example, must either change cams or accept a compromise in the manner in which the distribution of the roll density or hardness is controlled when changing the system from one size of roll to another or when winding different kinds of web materials since the shape of the cam is mechanically fixed.